This invention relates to battery manufacture.
Most batteries are constructed using a container, known as a can, that holds reactive chemicals that drive the battery by electrochemical reactions. The chemicals are usually divided by a separator. An electrolyte fluid facilitates ionic flow between the chemicals and across the separator to develop an electric potential.
Generally, alkaline batteries include a cathode, an anode, a separator, and an electrolytic solution. The cathode is typically formed of an active material (e.g., manganese dioxide), carbon particles, and a binder. The anode can be a gel including an active material (e.g., zinc particles). The separator is usually disposed between the cathode and the anode. The electrolytic solution, which is dispersed throughout the battery, can be a hydroxide solution. Alkaline batteries include the conventional AA, AAA, AAAA, C, and D batteries commonly sold in stores. These conventional alkaline batteries include a cylindrical container containing a central, cylindrical zinc gel anode surrounded by a thin separator, which is in turn surrounded by a ring-shaped cathode.
In the manufacture of alkaline batteries it is common to start with a cylindrical can to which is first added a pelletized cathode material that is in the shape of an annulus. A separator is then placed against the surface of the cathode inside the annulus. The separator may be a preformed cylindrical sheet of, e.g., cellulose material, or the separator may be material that is applied as a liquid and then forms a stable film. A small precharge of electrolyte is then added to wet the separator. The precharge is poured into the annular opening defined by the separator and forms a small pool at the bottom of the can from which it wicks into the separator after a period of time. After the pool has been substantially depleted by the wicking action, the anode material, typically a slurry containing, for example, zinc particles, is added to the opening. Allowing time for sufficient wicking is important so that addition of the anode slurry does not displace the pool and cause spillage of electrolyte over the top of the can.
In an aspect, the invention features a method for applying material in the manufacture of a battery including applying the material in the form of a spray generated from an vibratory nebulizer.
In another aspect, the invention features a method for applying electrolyte in the manufacture of a battery, including applying the electrolyte in the form of a spray.
In another aspect, the invention features a method for applying a separator in the manufacture of a battery, including applying a film-forming system that forms a film. The system includes a first component and a second component. The first and second component are applied simultaneously as a spray.
In another aspect, the invention features a method for applying material in the manufacture of a battery. The method includes selecting a material to be applied and applying the material in the form of a spray having an average droplet size of about 1 micron to about 75 micron less.
Embodiments may also include one or more of the following. The droplet size is about 5 micron to about 30 micron. The spray velocity is about 10 inch/sec or less, preferably about 3 to about 5 inch/sec. The method includes providing a separator and applying the electrolyte to at least one portion of the separator. The method includes providing the separator in a battery can prior to the applying the material by spraying. The method includes applying the electrolyte such that substantial pooling of the electrolyte in the bottom of the can is avoided. The spray is formed by an ultrasonic nebulizer. The material is a film-forming material suitable as a separator. The method includes providing a cathode and applying the film-forming material to at least a portion of the cathode. The method includes providing the cathode in a can prior to applying the film-forming material. The method includes facilitating film-forming by application of a second component, the second component being applied as a spray. The second component is applied sequentially with the film-forming material. For example, the second component may be supplied after application of the first component or the second component may be applied prior to the first component. The second component is applied simultaneously with the film-forming material. The film-forming material is PVA. The PVA is film formed by application of electrolyte. The PVA and electrolyte are applied sequentially. The PVA and electrolyte are applied simultaneously. The battery has a non-cylindrical electrode surface, such as a lobed surface, and the material, e.g. separator material, is applied as a spray originating near the axis of the battery. The battery is an alkaline battery.
Embodiments may provide one or more of the following advantages. Application of materials during battery manufacture by providing the materials in the form of a low velocity, small droplet spray can increase the uniformity of the application, reduce the time required for application, eliminate processing steps, and provide separators and other components with new and advantageous characteristics. For example, spray application of a precharge of electrolyte to a separator provides a highly uniform application of the electrolyte and also eliminates the need to await wicking of electrolyte from a pool of electrolyte that is formed by initially pouring a pre-shot of the electrolyte into the cavity prior to introduction of the anode slurry. Application of film-forming separator material in the form of a spray provides a highly uniform separator that is easily integrated into a manufacturing environment. A vibratory nebulizer, particularly ultrasonic nebulizers, provide substantial advantage in application of materials during battery manufacture. The drop size and velocity-tunable, generally low momentum mist or aerosol generated by such nebulizers allows a low velocity application without generating substantial turbulence or splattering in the tight confines of the battery can environment. Moreover, velocity and drop size can be adjusted. The nebulizer tip diameters are relatively small, making them applicable to the narrow diameter of a variety of battery can sizes.
Still further aspects, features, and advantages follow.
We first briefly describe the drawings.
Drawings
FIG. 1 is a schematic of a system for low velocity, small droplet spray application of materials in battery manufacture;
FIG. 2 is a cross-section of an ultrasonic nebulizer;
FIGS. 3, 3A, 3B, 3C, 3D and 3E are cross-sectional side views illustrating battery manufacture using application of materials as a spray;
FIGS. 4, 4A, 4B, 4C, 4D, 4E and 4F are cross-sectional side views illustrating another embodiment of battery manufacture; and
FIGS. 5, 5A and 5B are end-on views illustrating another embodiment of battery manufacture.